INTRODUCTION: Very elderly patients with nonvalvular atrial fibrillation (NVAF) are at high risk for both ischemic and hemorrhagic events. This study aimed to understand the characteristics and real-world treatment of very elderly patients with NVAF in Japan. METHODS: We conducted a retrospective analysis of electronic health records and claims data from acute care hospitals for very elderly patients with NVAF with medical records available on or after their 80th birthday. The outcomes of interest were (1) characteristics of very elderly patients and (2) patterns of anticoagulation and impact of clinical condition on anticoagulation. RESULTS: Of 1,278,404 patients with newly diagnosed atrial fibrillation (AF), 443,820 were eligible for the analysis. Mean ± standard deviation age was 84.5 ± 5.5 years, CHADS CONCLUSIONS: A significant proportion of very elderly patients with NVAF in Japan were diagnosed with NVAF after the age of 80 years and were not receiving anticoagulation therapy, particularly with increasing age. Furthermore, warfarin use declined with age, and patients on DOACs frequently received reduced doses.